A long-life incandescent electric lightbulb having a low frequency of replacement is desirable for many applications. This need has been met in the past with a variety of lightbulb design modifications.
Lightbulb filaments that operate at lower than normal temperatures have extended life. Unfortunately, low temperature filaments have reduced visible light output and are energy inefficient.
Other design modifications for increasing incandescent lightbulb life include the use of multiple filaments contained in one lightbulb envelope. U.S. Pat. Nos. 3,260,888, 3,983,447, and 2,317,027 are representative of such multiple filament designs. These bulbs have the common feature of an active filament and an unused filament. These prior art multiple filament devices require in each case active intervention by a user to activate the unused filament upon destruction of the original active filament. Such user intervention is often inconvenient and may be impractical when the lightbulb is in a remote location.